The present invention relates to an objective lens driving apparatus used in an optical data recording and reproducing apparatus or the like, for correcting a focusing error and a tracking error of a light spot formed on an optical data recording media such as an optical disk.
In the optical data recording and reproducing apparatus or the like, the data is recorded on and/or reproduced from the optical data recoding media (hereinafter, referred to as a recording media) such as the optical disk. In order to record the data on and/or reproduce the data from the recording media, the focus of an objective lens must be adjusted on a groove or a pit in which the data is recorded, and the light spot must be positioned on a track. Therefore, it is necessary to precisely control the position of the objective lens in the direction parallel to the optical axis of the objective lens and in the direction traversing the track of the recording media. Japanese Provisional Patent publication No. HEI 6-79383 discloses an objective lens driving apparatus for controlling the position of the objective lens.
FIG. 16 shows the objective lens driving apparatus disclosed in the above publication. The objective lens driving apparatus has a lens holder 101 that holds an objective lens 102. The lens holder 101 is supported by a support shaft 107 extending in parallel to the optical axis of the objective lens 102 so that the lens holder 101 is slidable along the support shaft 107 and rotatable about the support shaft 107. A pair of focusing coils 104 and a pair of tracking coils 103 are fixed to the outer surface of the lens holder 101. The focusing coils 104 are symmetrically located with respect to the support shaft 107, and the tracking coils 103 are symmetrically located with respect to the support shaft 107.
An outer yoke 109 and an inner yoke 105 are provided around the lens holder 101. Arc-shaped magnets 106 are fixed to the inner surface of the outer yoke 109. As shown in FIG. 17 in an enlarged scale, each magnet 106 has a focusing magnet portion 106a and a tracking magnet portion 106b. The focusing magnet portion 106a and the tracking magnet portion 106b are divided by a groove 106c formed at an intermediate position of the magnet 106. The focusing magnet portion 106a is polarized in such a manner that the N-pole and the S-pole are arranged in the direction parallel to the support shaft 107. The tracking magnet portion 106b is polarized in the direction perpendicular to the polarization of the focusing magnet portion 106a. 
Magnetic pieces 110 are secured to the outer surface of the lens holder 101 in such a manner that each of the magnetic pieces 110 is aligned with a border between the N-pole and the S-pole of the focusing magnetic portion 106a. The magnetic piece 110 is an elongated member extending in the direction parallel to the support shaft 107.
In order to correct the focusing error, current is applied to the focusing coils 104. The interaction between the current and the magnetic field caused by the focusing magnet portions 106a generates an electromagnetic force for moving the lens holder 101 in the direction parallel to the optical axis of the objective lens 102. As a result, the objective lens 102 is moved in the direction parallel to the optical axis thereof, so that the focusing error is corrected. In order to correct the tracking error, current is applied to the tracking coils 103. The interaction between the current and the magnetic field caused by the tracking magnet portions 106b generates an electromagnetic force for rotating the lens holder 101 about the support shaft 107. As a result, the objective lens 102 is moved in the direction traversing the track of the recording media, so that the tracking error is corrected.
As the lens holder 1 moves or rotates, a magnetic attractive force is exerted between the magnetic piece 110 and the focusing magnet portions 106a. With the magnetic attractive force, the lens holder 101 is stably held at a reference position in the direction parallel to the optical axis of the objective lens 102 and a reference position in the direction of the rotation about the support shaft 107.
However, since the above described conventional objective lens driving apparatus uses two kinds of magnet portions respectively for focusing and for tracking, the structure (including a polarization structure) of the magnet becomes complicated, and the number of components increases. Therefore, the conventional objective lens driving apparatus has a problem that the manufacturing cost increases, and the manufacturing process becomes complicated.
Moreover, in the above described conventional objective lens driving apparatus, the lens holder has a backlash because of a gap between a bearing portion of the lens holder 101 and the support shaft 107. Such a backlash of the lens holder 1 may result in tilt and vibration of the objective lens 102.